Tire pressure transducers are mounted on a wheel inside a tire and detect air pressure within the tire. An air pressure transducer includes a radio frequency transponder that responds to received radio frequency signals. A computerized automobile monitoring system for a vehicle on which the tire is mounted transmits a radio frequency poling signal and the pressure transducer responds by communicating the detected pressure back to the automobile monitoring system. A different pressure transducer is located within each tire, thus making the tire pressure for each tire on a vehicle available to the automobile monitoring system.
Wheel mounted tire pressure transducers are expected to attain increasing importance as time goes by. Because improperly inflated tires can lead not only to excessive tire wear, but also to tire damage that can cause a high speed blow out, wheel mounted tire pressure transducers are becoming an important safety device on many automobiles.
The pressure transducers are presently mounted within a small box or container that is secured to a fastener in the form of a valve stem that controls moving air into and out of the tire in a conventional manner. On a single piece wheel the pressure transducer is mounted inside the tire with the valve stem portion extending through a valve stem hole in the wheel to provide access connection to an air nozzle. The valve stem hole on a one pieces wheel is located at least partially on a side wall of the wheel so that the transducer extends into the wheel drop and tire containment space at an angle relative to the cylindrical center region of the wheel. That is, the pressure transducer extends neither parallel to the central axis of the wheel nor radially outward relative to the central axis. Consequently, the pressure transducer is radially spaced from the wheel center cylinder but does not extend radially outward beyond the rim of the wheel and does not interfere with the mounting of the tire on the wheel or the flexing of the tire when the automobile is being driven.
This mounting technique is satisfactory for single piece wheels, but is not adequate for multi-piece wheels. Multi-piece wheels, which are typically high performance alloy wheels, have a modular design with two or three pieces being bolted together to form the complete wheel. Such multi-piece wheels are required to have the valve stem hole located in a central, cylindrical part of the wheel and extend radially through the wheel. Such a radial mounting causes the pressure transducer to extend too far radially outward from the central cylindrical portion of the wheel and beyond the outer radius of the wheel rim, thus interfering with flexure and mounting of the tire and incurring possible damage in the event of a flat tire.
Two different mounting techniques have been used to mount a pressure transducer within a multi-piece wheel. Neither technique is fully satisfactory. One technique is to simply weld the pressure transducer to a central portion of the wheel. This technique avoids the radial over extension problem but makes it difficult or impossible to move the relatively expensive pressure transducer from one wheel to another in the event that a wheel is exchanged because of a flat tire, because a new set of wheels have been purchased or for some other reason. Another technique is to secure the transducer to the central cylindrical portion of the wheel by a strap that extends around the circumference of the central portion of the wheel. Such a strap is subject to stretching and slippage under the centrifugal force of high speed wheel rotation and adds unwanted mass to the wheel.
A need thus exits for an inexpensive, low mass, reliable pressure transducer mounting assembly that properly secures the pressure transducer to a wheel, but allows the pressure transducer to be easily transferred to a different wheel when appropriate.